The objectives of this research proposal are to elucidate the regulatory mechanisms of circadian rhythms in metabolic rate and body temperature (Tb) during sleep and wakefulness in the pigeon. The working hypothesis is that nocturnal Tb is regulated during sleep at a level proportional to the bird's energy reserves. This Continuation Proposal has two specific aims: (1) To investigate whether the proportional regulation of Tb and metabolic rate is sleep-dependent or under a circadian control independent of sleep itself, since the circadian rhythms of Tb and MR could be synchronized with those of sleep through a mutual entertainment by the light-dark cycle. To evaluate these alternate hypotheses, pigeons will be subjected to three different photoperiods: (a) 12:12 light-dark cycle (LD), (b) continuous dim red light (DD), and (c) continuous bright light (LL) presented in a schedule of five consecutive conditions: LD, 21 days; LL, 21 days; DD, 21 days; LL 21 days; LD 2 days. Birds will also be subjected to a 4-day fast during the first three conditions. Tb, body weight (BW), behavioral activity (ACT) and feeding (F) will be continuously recorded, and 24-hr electrophysiological recordings taken at frequent intervals. Raster and spectral plots of Tb, BW, ACT, F and sleep stages in each condition will be compared. Stages of sleep and EEG Fourier spectral analyses will be compared between nutritional and photoperiodic conditions, and across transitions from LL to DD and from LL to LD to assess possible compensatory recovery of sleep after extended wakefulness in LL. (2) To explore the potential roles of melatonin and beta-hydroxybutyrate (beta-OHB) as metabolic regulatory factors involved in the control of the circadian rhythms of sleep and Tb. Pigeons provided with ad lib food and water will be exposed to LL until circadian rhythms of TB and sleep have disappeared. i.v. infusions of melatonin will then be administered for 12- hr periods each day to determine whether melatonin reinstates and entrains circadian rhythms of Tb and sleep. Control infusions of saline will be administered subsequently. Circadian patterns of serum concentrations of beta-OHB -- a ketone metabolite of lipolysis -- will be assayed during 4- day fasts in pigeons exposed to a LD. These proposed experiments should further delineate a model of circadian regulation of Tb and sleep. Establishment of additional physiological homologies between sleep, circadian torpor and hibernation should elucidate sleep functions, and might lead to clinical applications in the treatment of disorders of sleep and regulation of body weight, diabetes, and depression.